I currently have a total of $18,000 on two CCs (Virgin Money and Coles/GE) as 0% balance transfers, which has been invested in an online account earning around 6% pa. Both these cards mature soon ($6K next week and $12K in March), so it was very timely that one of my other CC accounts (from Bankwest, which I originally opened in order to get a free $100 credit on the account, but don't normally use) sent me an offer to do a balance transfer of up to 95% of my credit limit at 0% for 6 months. I'll take out a $13,500 balance transfer on this card and invest the funds at 6% for the next 6 months, earning $405 for about ten minutes "work".
I still haven't sent in the other new CC app that arrived from HSBC a few weeks ago - I need to complete the application form and send it in tomorrow. I only requested a $10K balance transfer on the application as I don't know what credit limit they'll give me.
Assuming the new card is approved I'll have a total of $23.5K invested at 6% for the next 6 months and I'll have earned around $1,250 interest on OPM in 12 months. Even after paying tax at my marginal rate it will have been worth the small amount of time and trouble involved in getting the cards, applying for the balance transfers, setting up automatic payments of the card minimum payments each month, and shifting funds around at the start and end of the balance transfer period. As I keep the balance transfer amounts invested in an online bank account available at call there's no significant risk involved.